1. Field of the Invention
The present invention relates to a single flank tester, particularly capable of measuring the transmission error taking place between the gears meshed with each other with a high resolution even at a rotational speed close to that used in the desired application.
2. Description of the Prior Art
FIG. 1 shows a block diagram of the conventional single flank tester.
In FIG. 1, the two gears to be tested 1 and 2 are respectively mounted on the shafts 11 and 21, making one body therewith, whereby in order that the two gears 1 and 2 are meshed with each other at a certain determined distance between the centers of the gears, the shafts 11 and 21 are rotatably held on the bearings (not shown in the drawing) at a certain distance between them. The shaft 11 projects on both side of the gear 1, whereby the rotation shaft of the motor 3 is connected to the end of the one projecting shaft (the left projecting shaft in FIG. 1). In consequence, when the motor 3 is rotated at n(rps), the gear 1 is also rotated at n(rps). Supposing now that the tooth number of the gear 1 be Z1, while that of the gear 2 be Z2, the rotation number (Z1/Z2)n(rps) is transmitted to the gear 2. As explained above the gear 1 is driven by means of the motor 3 while the rotation number is transmitted to the gear 2, so that hereinafter the gear 1 is called the driving gear, while the gear 2 is called the driven gear.
12 and 22 are the pulse generators, being mounted on the shaft 11 of the driving gear 1 respectively on the shaft 21 of the driven gear 2. The pulse generators 12, 22 consist of, for example, of a slit disc secured on the shaft and two sets of a light source and a phototransistor, whereby the light source and the phototransistor are diametrically opposed with reference to the slit disc. The slit disc is provided with P slit at an equal distance between adjacent ones, while one set of a light source and a phototransistor is mounted at a first position and the other set if displaced at a distance of 1/4 of the adjacent slit spacings. As a consequence, the phototransistors produce P signals per rotation of the shafts, whereby the phase of the one signal is shifted from the other by 90.degree.. Thus, the signals are led to the multiplier circuit provided inside or outside of the pulse generators 12 and 22 so as to be multiplied with m and shaped in pulse forms in such a manner that mP pulse signals are produced per rotation of the shaft.
As a consequence, when the motor 3 rotates at n(rps), the shafts 11 and 21 rotate at n(rps), and respectively (Z1/Z2)n(rps), so that the frequencies f1 and f2 of the pulse signals produced with the pulse generators 12 and 22 are as follows. ##EQU1##
The pulse signals produced with the pulse generators 12 and 22 are led to the tooth number compensation circuits 13 and 23. The tooth number compensation circuit 13 consists of a frequency dividing circuit, whereby the frequency dividing ratio is set at the reciprocal value of the number of teeth in the other gear meshed with the gear it is associated with. Thus, the frequency dividing ratios of the tooth number compensation circuits 13 and 23 are respectively 1/Z2 and 1/Z1. Consequently, the pulse signals produced by means of the pulse generators 12 and 22 are multiplied by 1/Z2 and 1/Z1 by the frequency division in such a manner that the frequencies f1' and f2' delivered from the tooth number compensation circuits 12 and 22 become equal to each other as follows. ##EQU2##
Thus, the conversion into the two pulse signals of the same frequency (f1', f2') means that every time the gears 1 and 2 rotate a certain determined equal distance on the intermeshing pitch circle along which the driving gear 1 and the driven gear 2 are intermeshed, one pulse signal is produced by each compensation circuit. Thus, in case there is a transmission error between the gears 1 and 2, a phase difference proportional to the transmission error occurs between the two pulse signals of the same frequency (f1', f2').
Below, how to obtain the transmission error between the gears 1 and 2 out of the measured phase difference will be explained.
The phase difference is proportional to the phase difference time between the two pulse signals and reciprocal to the period of the pulse signal. In other words, the phase difference is proportional to the product of the phase difference time and the frequency of the pulse signal. The reason is that the phase difference time is one half of the time between pulses when the frequency of the pulse signal is two times as large (period: 1/2) even when the phase difference is same. Consequently, in order to obtain the phase difference, the phase difference time between the two pulse signals of the same frequency (f1', f2') produced by means of the tooth number compensation circuits 13 and 23 must be obtained, whereby the pulse signal with the frequency f1 produced by means of the pulse generator 12 is put in the phase difference time interval so as to count the interpolated pulse number. However, the ratio of the pulse signal with the frequency f1 for interpolation with that (f1', f2') for obtaining the phase difference time interval is, as is clear from the equation (2), the number of teeth (Z2) of the driven gear 2, so that when Z2 is small, the ratio is also naturally small. Thus, the number of the pulse signals with the frequency f1 to be interpolated in the phase difference time interval becomes also remarkably small for the above mentioned calculation method. In order to avoid this, the pulse signals of the same frequency (f1', f2') produced by means of the tooth number compensation circuits 13 and 23 are at first led to the frequency dividing circuits 14 and 24 so as to be divided with a same corresponding frequency dividing ratio 1/l in order that the frequency f1', f2' is stepped down to f1'/l, f2'/l. Then, the two pulse signals with the frequency (f1'/l, f2'/l) are led to the gate control circuit 4 consisting, for example, of a flip-flop circuit so as to produce the one signal for opening the gate with the pulse signal f1'/l and the other signal for closing the gate with the pulse signal f2'/l. Consequently, the phase difference time between the two pulse signals with the same frequency f1'/l, f2'/l is converted into the opening time interval of the gate control signal, hereby being multiplied with l. Then, by means of the gate control signal the gate circuit 5 is made conductive in such a manner that the pulse signals with the frequency f1 led from the pulse generator 12 pass through the gate 5 during the phase difference time. Hereby, the pulses which have passed through the gate 5 are counted by means of the counter 6, whereby the value counted by means of the counter 6 is latched with the latch circuit 7 every time a pulse signal with f1'/l delivered from the frequency dividing circuit 14 is applied to the latch circuit 7 in such a manner after every latching the counter 6 is reset at "0" so as to start the next counting.
Thus, in the latch circuit 7, the product of the phase difference time between the two pulse signals with the same frequency (f1'/l, f2'/l) with the frequency f1 of the pulse signal produced with the pulse generator 12 so as to be proportional to f1'/l, namely the number of pulses proportional to the phase difference is latched. As explained above, this phase difference is proportional to the transmission error taking place between the gears 1 and 2, namely, the transmission error is obtained from the number of the pulses latched with the latch circuit 7.
However, in case of the above mentioned device, the phase difference is obtained by interpolating the pulse signals delivered from the pulse generator into the phase difference time interval between the pulse signals, which is restricted as follows. Namely, the measurement resolution of the phase difference is determined with the number of pulses P produced by means of the pulse generator 1 per rotation and the multiplying ratio m, namely 360/mP(deg.). Consequently, in order to raise the resolution it is necessary to make m and P as large as possible, whereby it is difficult to make the multiplying ratio correctly so that after all it is necessary to make P larger.
For example, when it is desired to measure the transmission error with the resolution X=1/1200 (deg.) [=3 (sec.)] when the multiplying ratio m of the pulse generator is 4 (the multiplying ratio of 4 is obtained by taking out a pulse at every leading edge and falling edge of the two signals having a phase difference of 90.degree. between each other), it is necessary that the number of pulses P produced by means of the pulse generator per rotation is 108,000 as follows: ##EQU3##
If the number of the pulses generated by means of the pulse generator becomes very large as mentioned above, it is difficult to raise the number of rotations of the shaft of the pulse generator, namely the number of rotations of the gear connected to the shaft of the pulse generator so as to be tested, this parameter being handicapped by the response time of the phototransistor. Generally speaking, the frequency at which the phototransistor can make response, namely the maximum frequency that the pulse generator is allowed to produce is about 100 KHz. Consequently, the maximum number of rotations of the pulse generator is restricted to about 55 rpm, which means the gears are unavoidably tested within the range of rotation number by far smaller than the practical one, which is very inconvenient.